As integrated-circuit devices scale smaller, higher-resistance metals, such as cobalt, are being used as vias to connect copper interconnects. The higher-resistance metals, however, increase the overall resistance of an interconnect structure, thereby adversely impacting the performance (i.e., the RC delay) and the reliability of the integrated device. The resistance of conventional dual-damascene copper via especially increases rapidly with device scaling and may exceed the resistivity of a pure cobalt via. In this case, cobalt may be considered as a via material.